Hi I just made a glass gauge for mouthpiece refacing I used clear screen
printing film between two glass slides 2" by 3" the slides are 1.2 mm
thick each so their is no flex. The clear screen printing film is as
sharp as a film negative so their is no variance when printed the scale
is right on. I made the gauge because I found it hard to find one. I can
sell them for $8 + shipping  You can view it at mitchellstore.com
<http://mitchellstore.com/index.html>   Thanks